The automatically generated explanation isn’t -bad-.. but it lack depth. Still the automated explaination is good when you can’t get a human one.

The human explaination:
If I have no-one targeted and I’m not currently channeling a spell then hitting this macro will trigger Life Tap (rank 1) (triggering the Life Tap buff from the Life Tap Glyph).

If I have the tank (a friendly target) as my target and I hit this macro it will set my target to be the tank’s target (hopefully the mob we’re killing), if my pet isn’t currently attacking anything it will send my pet to attack that mob, and then cast Life Tap (rank 1) (triggering the Life Tap buff from the Life Tap Glyph).

If I have an unfriendly mob targeted, and if my pet isn’t currently attacking anything it will send my pet to attack that mob, and then cast Life Tap (rank 1) (triggering the Life Tap buff from the Life Tap Glyph).

If my pet is attacking something then hitting this macro will cast Life Tap (rank 1) (triggering the Life Tap buff from the Life Tap Glyph) and call my pet back to follow me.

ie, in a fight I target the tank and hit this macro to trigger my life tap glyph and to send my pet. I then hit the macro again to call my pet back to me.

On my hunter I have replaced “/cast [nochanneling] life tap(rank 1)” with “/cast Hunter’s Mark” to mark the target.